Telephone keypad

The development of the modern telephone keypad is attributed to research in the 1950s by Richard Deininger under the directorship of John Karlin at the Human Factors Engineering Department of Bell Labs.

[2][3] The modern keypad is laid out in a rectangular array of twelve push buttons arranged as four rows of three keys each.

For military applications, a fourth column of keys was added to the right for priority signaling in the Autovon system in the 1960s.

These keys were added to provide signals for anticipated data entry purposes in business applications, but found use in Custom Calling Services (CLASS) features installed in electronic switching systems.

"[5] Meanwhile, a 1960 paper – just five years later – refers to today's common calculator layout as "the arrangement frequently found in ten-key adding machines".

They were arranged as follows: Putting the letter O on the zero makes sense, as in British speech, "oh" is often said rather than "nought" or "zero"; Q is visually similar to O, and therefore the two might be confused.

Touchscreen phones have made these input methods obsolete, as the screens are typically large enough to show as many virtual buttons as necessary for a full keyboard.

Pressing a single key of a traditional analog telephone keypad produces a telephony signaling event to the remote switching system.

[14] Early smartphones such as the Palm Treo, HTC Wizard and BlackBerry had full alphanumeric keyboards instead of the traditional telephone keypads, and the user had to execute additional steps to dial a number containing convenience letters.

The latter typically include the ITU standard letters next to each number (and many Android phone use the 1 key to access voicemail and the zero to type a "+").